Hundreds of convictions for drug-driving may be unsafe, according to a leading criminal solicitor.

Dafydd Roberts, Head of Criminal Law at Gamlins Law, is acting for several clients who may have been convicted as a result of flawed testing procedures.

One client, Callum Flynn, lost his job as a civil engineer after being banned from driving for a year, forcing him to find temporary work just to meet his mortgage payments.

Mr Roberts, who is based in North Wales but acts for clients across the UK, says the issue concerns a number of different testing providers.

Following an independent review by The Forensic Science Regulator involving analytical data from a Section 5A Road Traffic Act 1988 case involving Δ9-Tetrahydrocannabinol (THC) at one lab, “a number of issues were raised in relation to quality control and evaluation of data”.

UKAS, the national accreditation body responsible for accrediting labs carrying out forensic toxicology work, is currently conducting a review of the sector to see if improvements to testing processes need to be made.

In the case of Callum Flynn, he was stopped by police close to his home in Towyn, North Wales, while driving to his local shop in July 2019.

Five months later on December 2, he discovered that he had been charged after test results claimed to show that he was above the legal limit for THC.

Callum said: “The whole thing was an horrendous experience. I hardly drink let alone do drugs, but the impact on my family life was enormous.

“I lost my job as a civil engineer because I was no use to my boss unless I could drive and I had to take a series of temp jobs just to be able to pay the mortgage. Without them, I would have lost my home.

“It also had an impact on my daughter who suffers from autism and needed to get to hospital in Liverpool for treatment.

“Thankfully, I’ve now got my old job back because my boss knew I was a grafter, but I’m still suffering with things like car insurance which has gone up because of the conviction.”

Dafydd Roberts said: “It is apparent that this is potentially a very big problem with the veracity of test results from several labs in question.

“We are currently acting for a number of clients whose lives have been turned upside down as a result of allegedly flawed testing procedures but the true scale of the problem could run to hundreds of cases.”

Over 11,600 people were found guilty of drug-driving in 2019, according to Government figures – an increase of 20% on the previous year.